This invention relates to vehicle engine controls and more particularly to an improved electronic control for limiting the maximum speed of an internal combustion engine and, optionally, for also limiting the maximum running speed of a vehicle in which the engine is operated.
It is sometimes either desirable or necessary to limit the maximum speed at which an internal combustion engine is operated. Typical early speed limiting systems used a centrifugal governor which gradually decreased the output power from an engine as the engine speed increased over a relatively wide range. Such systems were undesirable for engines used in motor vehicles since they greatly reduced the output power or acceleration available from the engine long before the maximum engine speed was reached. More improved systems function to limit the engine speed only when the engine is operating within a narrow range of the predetermined maximum speed. Such systems do not limit or restrict the output power from the engine until the engine is operating within the speed limiting range. One typical prior art system disclosed in U.S. Pat. No. 2,867,196, which issued Jan. 6, 1959 to Francis, involves the use of a vacuum modulator which controls the setting of a throttle valve within a high speed carburetor throat. A centrifugal mechanism is mounted on the rotating shaft of the ignition distributor to progressively block an orifice as the speed of the engine is increased over a narrow high speed range. As the orifice is blocked, the increasing vacuum moves a piston in the vacuum modulator to progressively close the carburetor throttle valve as the engine speed is progressively increased over the narrow speed regulating range. However, the installation of a system of this type on an engine requires the installation of a special ignition distributor.
Similar arrangements have been used for limiting the maximum speed at which a vehicle may be operated. U.S. Pat. No. 3,811,418, which issued May 21, 1974 to Sakakibara, discloses a vehicle speed limiting system in which a vacuum actuated piston or cylinder is connected to position a throttle valve within a high speed carburetor throat. Normally, the throttle valve is maintained fully open to permit the engine to operate under full power. When the vehicle exceeds a predetermined maximum speed, a speed responsive switch intercoupled with the vehicle's speedometer is closed. When the switch closes, a solenoid valve is energized to control vacuum in the vacuum cylinder, thereby causing the throttle valve to move to a position blocking the high speed carburetor throat. When the vehicle speed decreases below the predetermined maximum speed, the solenoid actuated valve is de-energized and the throttle valve opens to permit the engine to again operate at higher speeds. Since the speed responsive switch is either fully open or fully closed, hunting about the predetermined maximum vehicle speed as the throttle valve is alternately opened and closed will occur in a system of this type.
Generally, prior art engine speed limiters were operated either to control the maximum speed of the vehicle or the maximum operating speed of the engine. Such systems were not adaptable to controlling both the maximum engine speed and the maximum vehicle speed. However, at times it is desirable to take into account both the engine speed and the vehicle speed when controlling an engine. For example, take a vehicle which is driven at 70 mph when the engine is operating at 4000 rpm. If the engine is limited to operate at 4000 rpm and the engine does not reach its peak torque or horsepower output until 5000 rpm, for example, then the peak output power of the engine cannot be utilized in lower gear ranges, since the engine can never exceed 4000 rpm. On the other hand, if the engine is controlled to limit the maximum vehicle speed to 70 mph, it will be possible to exceed safe engine speed ranges in lower gear ranges without exceeding 70 mph.